function [p_A] =PBuild(P)
%建立压力项
%   此处显示详细说明
global num b own  c_s nei P_out V
p_A=zeros(num,3);
for i=1:nei(1)
    S=sqrt(sum((c_s(i,:)).^2));
    p_A(own(i+1),:)=p_A(own(i+1),:)+(P(own(i+1),:)+P(nei(i+1),:))*S/2;
    p_A(nei(i+1),:)=p_A(nei(i+1),:)+(P(own(i+1),:)+P(nei(i+1),:))*S/2;
end
%引入边界条件
for i=1:b.out(1)
    S=sqrt(sum((c_s(i+b.out(2)-1,:)).^2));
    p=P_out;
    p_A(own(i+b.out(2)),:)=p_A(own(i+b.out(2)),:)+p*S;
end
for i=1:b.in(1)
    S=sqrt(sum((c_s(i+b.in(2)-1,:)).^2));
    p=P(own(i+b.in(2)),:);
    p_A(own(i+b.in(2)),:)=p_A(own(i+b.in(2)),:)+p*S;
end
for i=1:b.sym1(1)
    S=sqrt(sum((c_s(i+b.sym1(2)-1,:)).^2));
    p=P(own(i+b.sym1(2)),:);
    p_A(own(i+b.sym1(2)),:)=p_A(own(i+b.sym1(2)),:)+p*S;
end
for i=1:b.sym2(1)
    S=sqrt(sum((c_s(i+b.sym2(2)-1,:)).^2));
    p=P(own(i+b.sym2(2)),:);
    p_A(own(i+b.sym2(2)),:)=p_A(own(i+b.sym2(2)),:)+p*S;
end
for i=1:b.cylinder(1)
    S=sqrt(sum((c_s(i+b.cylinder(2)-1,:)).^2));
    p=P(own(i+b.cylinder(2)),:);
    p_A(own(i+b.cylinder(2)),:)=p_A(own(i+b.cylinder(2)),:)+p*S;
end
p_A=p_A./kron(V,[1,1,1]);
end